1. Field of the Invention
The present invention relates to a light source of a non-self-luminous display device, and more particularly to a liquid crystal display device having a backlight which includes a light guide plate and uses an LED as a light source.
2. Background Art
Recently, the liquid crystal display device has been popularly used as a display device. Particularly, the liquid crystal display device is used as a display part of portable equipment because the liquid crystal display device is thin and light-weighted, and consumes small electric power.
However, the liquid crystal display device is not self-luminous and hence, the liquid crystal display device requires a lighting means. In general, as a lighting device which is used for the liquid crystal display device, a planar lighting device referred to as a backlight is popularly used. Conventionally, although a cold cathode fluorescent tube has been used as a light emitting element (also referred to as a light source) of the backlight, an LED (light emitting diode) has been also recently used as the light emitting element.
The backlight includes a plate-shaped light guide plate. A material of the light guide plate is a light transmitting resin or the like, and light incident on the light guide plate from the light emitting element propagates in the inside of the light guide plate. A reflection/scattering member such as grooves, projections or a printed material is formed on the light guide plate, and the light which propagates in the inside of the light guide plate due to such a reflection/scattering member is directed and radiated toward a liquid-crystal-display-device side.
When the LEDs are used as the light emitting element, the LED is a spot light source and hence, there arises a drawback that the uniform radiation of light from the light guide plate is difficult. Accordingly, for example, JP-A-2007-121675 or the like proposes a technique which uniformly diffuses light of LEDs which constitute a spot light source, wherein the constitution which forms conical lenses on an optical sheet is disclosed. However, in the technique described in patent document 1, the lenses are formed on the optical sheet but are not directly formed on the light guide plate. Further, JP-A-2001-296407 discloses a meandering lens. However, the lens is formed on an optical sheet but is not directly formed on the light guide plate.